The present invention relates to an ink jet recording head driving method and a circuit therefor which drives an ink jet recording head incorporating a piezoelectric actuator. More particularly, the present invention relates to an ink jet recording head driving method and a circuit therefor, capable of enhancing the gray scale quality of characters and picture images by changing a diameter of micro ink droplets, which are discharged from nozzles, by use of gray scale information of printing data, and thus changing a size of dots formed on a recording medium such as paper and OHP (overhead projector) film.
An ink jet printer is provided with a plurality of nozzles and records characters and image pictures on a recording medium such as paper or OHP film by selectively discharging equal-sized micro ink droplets, which are fitted to a recording resolution, from each of the nozzles. Particularly, a drop on demand type ink jet printer, which records characters and image pictures by discharging only the ink droplets necessitated for recording characters and image pictures from nozzles, has been extensively used at home and offices since it is easily miniaturized and colorized as well as generates little noise. In order to attain higher-quality characters and image pictures by use of the aforementioned ink jet printer, a gray scale printing is effective, which changes the size of dots formed on a recording medium by modulating a diameter of micro ink droplets discharged from nozzles according to gray scale information of printing data.
FIG. 16 is a block diagram showing an example of electric configuration of an ink jet recording head driving circuit applied to the aforementioned conventional ink jet printer (hereafter, referred to as xe2x80x9cfirst prior artxe2x80x9d). FIG. 17 is a sectional view showing an example of mechanical configuration of relevant part of an ink jet recording head 1. FIG. 18 is a plan view showing an example of mechanical configuration of relevant part of an ink jet printer.
The ink jet recording head 1 of the example has a laminated structure comprising a nozzle plate 3 provided with a plurality of nozzles 2 (orifices), a pressure generating chamber plate 5 which is provided concavely with a plurality of pressure generating chambers 4, 4, . . . having one-to-one correspondence to each of the nozzles 2 and filled with ink supplied from an ink tank (not shown) through both an ink pool (not shown) and an ink outlet 5a, a plurality of diaphragms 6, 6, . . . having one-to-one correspondence to the pressure generating chambers 4 and forming a bottom plate for each of the pressure generating chambers 4 and a plurality of piezoelectric actuators 7, 7, . . . attached to each of the diaphragms 6 respectively. Electrodes 8 and 9 are mounted at both edges of each of the piezoelectric actuators 7. One of the electrodes 8 and 9 is earthed through an electrode line 10 and the other is connected to a switching unit 24 shown in FIG. 16 through the electrode line 10. This ink jet recording head is a drop on demand type multi head and, in particular, referred to as a Kyser type within the head. According to such an ink jet recording head, when drive waveform signals are applied from the switching unit 24 to arbitrarily combined piezoelectric actuators 7, 7, . . . according to printing data, the piezoelectric actuators 7, 7, . . . displace the corresponding diaphragms 6. Accordingly, the volume of the pressure generating chamber 4 therein ink is filled is rapidly changed and thus an ink droplet 11 is discharged from the corresponding nozzle 2.
As shown in FIG. 18, according to the ink jet printer of the aforementioned example, the ink jet recording head 1 is mounted on a head guide axis 12 so that it is sidable in the right and left direction in the figure, and is driven by a head drive motor (not shown). Meanwhile, a recording medium 13 such as paper or OHP film is moved in the up and down direction in the figure by a feed roller 14 driven by a feed motor (not shown). Hereafter, moving direction of the ink jet recording head 1 is referred to as a main scanning direction, and that of a recording medium 13 as a sub-scanning direction.
An ink jet recording head driving circuit shown in FIG. 16 is schematically configured comprising a control unit 21, a drive waveform storage means 22, a waveform generating unit 23 and a switching unit 24. The control unit 21, according to commands supplied from outside, controls a head drive motor which drives the ink jet recording head 1 and a feed motor which drives a feed roller 14. At the same time, the control unit 21 supplies a nozzle selecting data DSN to the switching unit 24 at every discharging period which denotes an adequate period when the ink drop 11 should be discharged from each the nozzle 2. A nozzle selecting data indicates an appropriate piezoelectric actuator 7 out of a plurality of piezoelectric actuators 7, 7, . . . whereto drive waveform signals comprising waveform shown in FIG. 19 should be applied. Incidentally, at the adequate timing, the control unit 21 supplies a discharging start command which denotes a command to start discharging the ink droplet 11 from each nozzle 2 to the waveform generating unit 23. The drive waveform storage means 22 is, for example, composed of ROM and the like and stores drive waveform information on drive waveform signals which should be applied to a plurality of piezoelectric actuators 7, 7, . . . .
The waveform generating unit 23 comprises waveform generating circuits 25, power amplifying circuits (not shown) and the like. After the waveform generating circuit 25 generates drive waveform signals on the basis of drive waveform information which is read out from a drive waveform storage means 22, the power amplifying circuit amplifies power, and then the amplified drive waveform signals are supplied to the switching unit 24 on the basis of a discharging start command sent from the control unit 21. The switching unit 24 comprises such as nozzle selecting circuits 26 and switches 27, 27, . . . composed of transfer gates, for example, and provided to be corresponding to piezoelectric actuators 7, 7, . . . . On the basis of the nozzle selecting data DSN supplied from the control unit 21, the switching unit 24 turns on any one of the switches 27, and applies drive waveform signals supplied from the waveform generating unit 23 to the corresponding piezoelectric actuators 7.
In the ink jet printer with the aforementioned configuration, the control unit 21 controls a head drive motor which drives the ink jet recording head 1 and a feed motor which drives a feed roller 14 according to commands provided from outside. At the same time, the control unit 21 supplies a nozzle selecting data DSN to the switching unit 24 at every discharging period and supplies a discharging start command to the waveform generating unit 23.
Accordingly, the ink jet recording head 1 is moved in the main scanning direction, while the recording medium 13 is moved in the sub-scanning direction. After the waveform generating circuit 25 generates drive waveform signals on the basis of drive waveform information read out from the drive waveform storage means 22, a power amplifying circuit amplifies power signals. Thus, the amplified drive waveform signals are supplied to the switching unit 24 on the basis of a discharging start command sent from the control unit 21. The nozzle selecting circuit 26 turns on any one of the switches 27 on the basis of the nozzle selecting data DSN supplied from the control unit 21. In this way, drive waveform signals supplied from the waveform generating unit 23 are applied to the piezoelectric actuators 7.
As a result, the ink droplet 11 is discharged from the nozzle 2 corresponding to a piezoelectric actuator 7 whereto drive waveform signals are applied. As shown in FIG. 20, in the recording medium 13, a dot which is slightly larger than one pixel of recording resolution (the area surrounded by four lines) is formed.
Repeating the aforementioned operations, many dots are to be formed on the recording medium 13, and thus characters or picture images are recorded. In this case, the nozzle 2 goes through an arbitrary pixel position on the recording medium 13 only once. Hereafter, the phenomenon that the nozzle 2 goes through an arbitrary pixel position on the recording medium 13 is simply referred to as xe2x80x9cscan(ning)xe2x80x9d.
According to the art disclosed in the Japanese Patent Application Laid-Open Nos. HEI 4-118245 and HEI 9-174884, one dot is formed by spotting a plurality of micro ink droplets, whereof sizes are standard or smaller in comparison with recording resolution, on one and the same place or around the place on a recording medium, and thus gray scale of picture images is expressed in accordance with the number of spotted ink droplets (hereafter, referred to as xe2x80x9csecond prior artxe2x80x9d).
Further, according to the art disclosed in the Japanese Patent Application Laid-Open No. HEI 4-361055, which is provided with a plurality of nozzles having a variety of ink droplet volumes, one pixel is formed by re-spotting ink droplets having a variety of volumes on one and the same place by repeating scanning, and thus gray scale recording is executed (hereafter, referred to as xe2x80x9cthird prior artxe2x80x9d).
Still further, according to the art disclosed in the Japanese Patent Application Laid-Open No. HEI 9-164706, which is provided with a plurality of nozzle line groups having a variety of nozzle diameters, points with a variety of dot diameters are formed on one and the same place of a recording medium through one scanning by exclusively driving those nozzles that have different diameters out of a plurality of nozzle lines (hereafter, referred to as xe2x80x9cfourth prior artxe2x80x9d).
Additionally, according to the art disclosed in the Japanese Patent Application Laid-Open No. HEI 10-81012, drive waveform signals outputted at every printing period are comprised of a first pulse which discharges ink droplets of medium dots, a second pulse which discharges ink droplets of small dots, a third pulse which discharges ink droplets of medium dots and a fourth pulse which gives micro-vibration to meniscus. By selecting one or some of the first to four pulses on the basis of gray scale value, dots having different diameters are formed on a recording medium, and thus gray scale printing is realized (hereafter, referred to as xe2x80x9cfifth prior artxe2x80x9d).
Furthermore, the art disclosed in the Japanese Patent Application Laid-Open No. HEI 9-11457 comprises a common waveform generating means which generates four kinds of drive waveform signals corresponding to a total of four cases; the cases of forming dots with three sizes and the case of not discharging ink, a recording means which records multi-valued printing data by converting the data into one fixed output, a signal processing means which signal-processes output of a recording means by use of a fixed format, and a multiplexer which makes one of the four transfer gates into the conducting state by using control signals formed by level-converting output of signal processing means and applies one of the four kinds of drive waveform signals to a piezoelectric actuator, and thus gray scale printing is realized (hereafter, referred to as xe2x80x9csixth prior artxe2x80x9d).
Meanwhile, in order to realize gray scale printing by use of the ink jet recording head driving circuit of the aforementioned first prior art, an ink jet recording bead 1 had to change drive waveform signals and repeat scanning at the same pixel position only number of times necessitated for gray scale. Thus, it took extremely long time to execute recording.
Additionally, according to the aforementioned second prior art, in the same manner as first prior art, since it was necessary to repeat scanning at the same pixel position on a recording medium, it took extremely long time to execute recording. At the same time, since a large number of ink droplets are spotted on one pixel, especially in case of color recording, quality of recording image can be lowered by inviting cockring, widening of lines or bleeding (blur of ink).
Further, according to the aforementioned third and fourth prior arts, since the number of the necessitated nozzles corresponds to the gray scale number, the size of an ink jet recoding head can be enlarged. Additionally, since the same number of piezoelectric actuators and other parts as that of nozzles are necessitated, an ink jet recording printer can be high-cost owing to enlargement of the size and complication of the configuration.
Still further, according to the aforementioned fifth prior art, an ink jet recording head is driven so that a plurality of ink droplets having a variety of jet amounts are discharged from the same nozzle within an extremely short time of one printing period. However, in order to precisely discharge a plurality of ink droplets with a variety of jet amounts within a short time, a special-purpose structure can be necessitated for nozzles or pressure generating chambers which are incorporated in an ink jet recording head. Also, ink has to be developed so as to have special components capable of consecutively discharging ink droplets with a variety of sizes within a short time (e.g., flow resistance or surface tensile need to be devised). However, according the art disclosed in the Japanese Patent Application Laid-Open No. HEI 10-81012, there is no disclosure in reference to structure of nozzles or pressure generating chambers, or components of ink, but only to a generating means of drive waveform signals. For such a reason, the art disclosed in the Japanese Patent Application Laid-Open No. HEI 10-81012 has a problem of being unable to execute gray scale printing by forming dots with a variety of diameters on a recording medium.
Incidentally, according to the aforementioned sixth prior art, drive waveform signals corresponding to the gray scale number are outputted from a common waveform generating means on a steady basis. By selecting one of the drive waveform signals, making the corresponding transfer gate conductive and applying the drive waveform signal to a piezoelectric actuator, dots with a desirable size are to be formed on a recording medium through one scanning. However, the larger the number of gray scale will be, the larger the number of drive waveform signals generated by a common waveform generating means will be. At the same time, structure of a multiplexer (the same number of transfer gates as gray scale number are necessary) for selecting one of a plurality of drive waveform signals becomes complicated accordingly. Consequently, an ink jet printer can be high-cost owing to enlargement of the size and complication of the configuration.
The present invention was developed in order to solve the aforementioned problems and shortcomings, and an object of the present invention is to provide an ink jet recording head driving method and a circuit therefor capable of realizing high-quality gray scale printing within a short time by using an ink jet recording head having a simple and low-cost configuration and a general-purpose structure, and ink having common components.
The present invention according to claim 1 relates to an ink jet recording head driving method provided with a plurality of nozzles and a plurality of pressure generating chambers corresponding thereto, and comprises the steps of applying drive waveform signals to piezoelectric actuators provided at the positions corresponding to the pressure generating chambers in case of recording, rapidly changing the volume of pressure generating chambers filled with ink, discharging ink droplets from the plurality of nozzles and forming dots on a recording medium. The present invention according to claim 1 is featured in repeating a dot forming process for forming a plurality of dots on the recording medium, and the process comprises the steps of moving the ink jet recording head is moved in a first direction which is relatively orthogonal to the located direction of the plurality of nozzles concerning the recording medium, generating a plurality of drive waveform signals according to a jet amount of the ink droplets, selecting any one or none of the plurality of waveform signals for each of the plurality of nozzles according to gray scale information of printing data, and applying voltage to corresponding piezoelectric actuators, while the ink jet recording head is moved in a second direction which is relatively orthogonal to the first direction concerning the recording medium.
The present invention according to claim 2 relates to an ink jet recording head driving method claimed in claim 1, and is featured in that at least one of a plurality of drive waveform signals generated at the aforementioned dot forming process is different from any of a plurality of drive waveform signals generated at the previously executed dot forming process.
The present invention according to claim 3 relates to an ink jet recording head driving method claimed in claim 1 or 2, and is featured in that at the aforementioned dot forming process, drive waveform signals for discharging ink droplets with a large jet amount and those with a small jet amount are generated in combination.
The present invention according to claim 4 relates to an ink jet recording head driving method claimed in claim 1 or 2, and is featured in that a dot forming process for generating drive waveform signals discharging ink droplets with a large jet amount and those with a small jet amount are alternately executed.
The present invention according to claim 5 relates to an ink jet recording head driving method claimed in one of the claims 1 to 4, and is featured in that the aforementioned dot forming process is executed at least twice on one and the same place of the aforementioned recording medium.
The present invention according to claim 6 relates to an ink jet recording head driving method claimed in claim 5, and is featured in that at the aforementioned dot forming process, nozzles which are positioned at the different place from the nozzles used at the previously executed dot forming process pass the place opposed to one and the same place of the aforementioned recording medium.
The present invention according to claim 7 relates to an ink jet recording head driving method claimed in claim 5, and is featured in that at the aforementioned dot forming process, nozzles which are positioned at the same place as the nozzles used at the previously executed dot forming process pass the place opposed to one and the same place of the aforementioned recording medium.
The present invention according to claim 8 relates to an ink jet recording head driving method claimed in claim 6 or 7, and is featured in that combination of drive waveform signals selected at once of the dot forming process is determined on the basis of not only the number of times of the aforementioned dot forming process but also the number of times whereof the same or different nozzles pass the place opposed to one and the same place of the aforementioned recording medium.
The present invention according to claim 9 relates to an ink jet recording head driving method claimed in claim 8, and is featured in that the number of times of the aforementioned dot forming process but also the number of times whereof the same or different nozzles pass the place opposed to one and the same place of the aforementioned recording medium are determined on the basis of a high-speed printing mode which is set up for printing in high-speed and a high-quality image mode which is set up for printing in high-quality image.
The present invention according to claim 10 relates to an ink jet recording head driving circuit provided with a plurality of nozzles and a plurality of pressure generating chambers corresponding thereto, and comprises the steps of applying drive waveform signals to piezoelectric actuators provided at the positions corresponding to the pressure generating chambers in case of recording, rapidly changing the volume of pressure generating chambers filled with ink, discharging ink droplets from the plurality of nozzles and forming dots on a recording medium. The present invention according to claim 10 is featured in that an ink jet recording head driving circuit comprises a recording means which records drive waveform drive waveform information signals at each jet amount of the aforementioned ink droplets, a waveform generating means which generates a plurality of drive waveform signals on the basis of information on a plurality of drive waveforms, which are read out from the recording means, a control means which moves the ink jet recording head in a first direction which is relatively orthogonal to the located direction of the plurality of nozzles concerning the recording medium, and outputs waveform selecting signals indicating that, on the basis of gray scale information of printing data, any one or none of the plurality of drive waveform signals should be selected for each of the plurality of nozzles, and a drive means which applies voltage to the piezoelectric actuators by selecting none or any one of a plurality of drive waveform signals outputted from the plurality of drive generating means on the basis of the waveform selecting data, while the control means moves the ink jet recording head in a second direction which is relatively orthogonal to the fist direction concerning the recording medium, and repeats not only scanning of the ink jet recording head in the first direction but also outputting the waveform selecting data.
The present invention according to claim 11 relates to an ink jet recording head driving circuit claimed in claim 10, and is featured in that the aforementioned waveform generating means generates at least one drive waveform signal which is different from any of a plurality of drive waveform signals generated at the previous scanning at every scanning of the aforementioned ink jet recording head in a first direction.
The present invention according to claim 12 relates to an ink jet recording head driving circuit claimed in claim 10 or 11, and is featured in that the aforementioned waveform generating means generates drive waveform signals for discharging ink droplets with a large jet amount and those with a small jet amount in combination.
The present invention according to claim 13 relates to an ink jet recording head driving circuit claimed in claim 10 or 11, and is featured in that the aforementioned waveform generating means alternately generates a plurality of drive waveform signals for discharging ink droplets with a relatively large jet amount and those with a relatively small jet amount.
The present invention according to claim 14 relates to an ink jet recording head driving circuit claimed in one of the claims 10 to 13, and is featured in that the aforementioned control means executes at least twice of not only scanning in the first direction of the ink jet recording head but outputting the waveform selecting data on one and the same place of the aforementioned recording medium.
The present invention according to claim 15 relates to an ink jet recording head driving circuit claimed in claim 14, and is featured in that the aforementioned control means makes nozzles, which are positioned at the different place from the nozzles used for scanning of the ink jet recording head in the first direction, pass the place opposed to one and the first place of the aforementioned recording medium.
The present invention according to claim 16 relates to an ink jet recording head driving circuit claimed in claim 14, and is featured in that the aforementioned control means makes nozzles, which are positioned at the same place as the nozzles used for scanning of the ink jet recording head in the first direction, pass the place opposed to one and the same place of the aforementioned recording medium.
The present invention according to claim 17 relates to an ink jet recording head driving circuit claimed in claim 15 or 16, and is featured in that the aforementioned control means generates the waveform selecting data on the basis of the data, supplied from outside, concerning combination of drive waveform signals selected at not only once of scanning of the ink jet recording head in the first direction but also outputting the waveform selecting data.
The present invention according to claim 18 relates to an ink jet recording head driving circuit claimed in claim 17, and is featured in that combination of the drive waveform signals is determined on the basis of not only the number of times of scanning of the ink jet recording head in the first direction but also the number of times whereof the same or different nozzles pass the place opposed to one and the same place of the aforementioned recording medium.
The present invention according to claim 19 relates to an ink jet recording head driving circuit claimed in claim 18, and is featured in that the number of times of scanning of the ink jet recording head in the first direction but also the number of times whereof the same or different nozzles pass the place opposed to one and the same place of the aforementioned recording medium are determined on the basis of a high-speed printing mode which is set up for printing in high-speed and a high-quality image mode which is set up for printing in high-quality image.
The present invention according to claim 20 relates to an ink jet recording head driving circuit claimed in claim 15 or 16, and is featured in that the aforementioned control means determines the number of times of scanning of the ink jet recording head in the first direction but also the number of times whereof the same or different nozzles pass the place opposed to one and the same place of the aforementioned recording medium on the basis of a high-speed printing mode which is set up for printing in high-speed and a high-quality image mode which is set up for printing in high-quality image, and determines the combination of drive waveform signals selected at not only once of scanning of the ink jet recording head in the first direction but also outputting the waveform selecting data on the basis of the determined number of times of scanning of the ink jet recording head in the first direction and number of times whereof the same or different nozzles pass the place opposed to one and the same place of the aforementioned recording medium, and generates the waveform selecting data on the basis of the determined combination of the drive waveform signals.